In a component conveyance height controlling method according to the background art, a nozzle height is updated based on a mounting height of a component mounted on a board and a height of a component sucked by the nozzle. While the nozzle is holding and moving the electronic component, the nozzle is kept at a fixed height. The height to be taken into consideration is only the height of the electronic component. Particularly because the nozzle is not changed in height during moving, there is a problem that an elevating stroke of the nozzle for mounting the component after the nozzle has reached above the circuit board is large (e.g. See Patent Document 1).
In addition, there is another component conveyance height controlling method, in which a moving head is triggered to start to move horizontally as soon as a lower end portion of a nozzle which is moving up reaches a predetermined interference avoidance height. There is, however, no consideration about the operation for moving the nozzle down. Thus, there is a problem that an operation for moving the nozzle up and down is not optimized (e.g. See Patent Document 2).
There is further another component conveyance height controlling method, in which a plurality of nozzles are moved down and made to stand by at a height high enough not to interfere with mounted components and a plurality of the nozzles are then moved down to mount components. However, there is no consideration of the height of each nozzle before the nozzle reaches above a circuit board. Therefore, there is a problem that an elevating stroke of a first nozzle mounting a component is so large that no effect can be exerted unless the equipment is provided with a plurality of nozzles (e.g. see Patent Document 3).
A technique according to the background art will be described below in detail with reference to FIG. 12.
FIG. 12 is an example of the configuration of a component mounting apparatus for mounting a component by use of an XY robot. An XY robot 53 driven by an X-axis motor 51 and a Y-axis motor 52 is used. A mounting head 54 mounted on the XY robot 53 is disposed so as to be movable desirably in a horizontal plane. A nozzle 55 and a Z-axis motor 56 for moving the nozzle up/down desirably are attached to the mounting head 54. Electronic components are received in a component supply unit 57. A circuit board 58 is fixed by a pair of opposed conveyance rails 59. One cycle of electronic component mounting operation includes a component suction operation, a component recognition operation, and a component mounting operation. In the component suction operation, the nozzle 55 moves above the component supply unit 57 and descends to pick up an electronic component from the component supply device 57. In the component recognition operation, the nozzle 55 moves above a component camera 60 so as to photograph the posture of the electronic component through the component camera 60. In the component mounting operation, the nozzle 55 moves above the circuit board 58 and descends to mount the electronic component on the circuit board 58. Such a cycle of the electronic component mounting operation is performed repetitively so as to mount a plurality of electronic components. A board camera 61 for photographing the position of the circuit board is provided in the mounting head 54 and used for checking the position of the circuit board 58 prior to component mounting. Spare nozzles are received in a nozzle station 62. In order to correct the position of the mounting head 54, a reference mark 63 capable of being photographed by the board camera 61 may be provided.
Since it is necessary to locate the aforementioned component camera 60, nozzle station 62 and reference mark 63 in a movable range of the mounting head 54, the aforementioned component camera 60, nozzle station 62 and reference mark 63 are usually disposed between the circuit board 58 and the component supply unit 57. In the configuration as shown in FIG. 12, there is a possibility that the nozzle 55 may pass over the component camera 60, the nozzle station 62, the reference mark 63 and one of the conveyance rails 59 before the nozzle arrives above a component mounting position on the circuit board 58 after the nozzle has picked up a component from the component supply unit 57 and recognized the component through the component camera 60. These component camera 60, nozzle station 62, reference mark 63 and conveyance rails 59 are disposed respectively in required positions and at required heights, but not allowed to be moved easily in order to ensure accuracy. Accordingly, a height high enough not to interfere with each of these obstacles (the component camera, the nozzle station, the reference mark, and the conveyance rail) has to be ensured as the height with which the nozzle 55 moves.
(Patent Document 1) Japanese Patent Publication JP-A-9-214182/(1997)
(Patent Document 2) Japanese Patent Publication JP-A-2002-111284
(Patent Document 3) Japanese Patent Publication JP-A-11-330786/(1999)